Print hammer bank in modular design

ABSTRACT

The invention relates to a print hammer bank of electromagnetic print hammer actuators in modular design of the type which includes a plurality of actuators each of which comprises a stator formed in two halves, each half including an electromagnet and a plurality of pole pieces, and means for positioning the stator halves relative to each other so that the ends of the pole pieces of the two halves are spaced apart in pairs so as to form a plurality of aligned operating gaps. The armature elements are designed so that the volume of each armature element is of the order of the volume of the associated operating gap. 
     A print hammer bank in accordance with the invention is characterized in that the print hammer bank consists of two spaced apart rows of modules of the same geometrical shape and design forming the stator halves with the armature members located side by side in the space between the rows of modules, in that, for adjacent print hammers, the associated electromagnets are staggered relative to each other within the associated module, and in that each module, looking at the side facing the armature members, is shaped like a parallelogram.

FIELD OF THE INVENTION

The present invention relates to impact printers of the type including abank of electromagnetic hammers which are actuated selectively in orderto perform printing operations on a print medium, for example a sheet ofpaper.

The present invention relates to the construction of such a print hammerbank.

BACKGROUND OF THE INVENTION

The present invention relates to electromagnetic print hammer actuatorsof the type described in the Canadian Pat. No. 1135317 particularly withreference to FIGS. 1a, 1b, 2, 3, 4 and 6.

Hammer actuators in the Canadian Patent comprise a stator and a movablearmature member or ram that forms the hammer. The stator consists of twosubstantially symmetrically constructed magnetizable yoke halves withone or more excitation coils. Each yoke half is formed with two or morepole pieces. The yoke halves are positioned so that the ends of the polepieces of one yoke half are aligned with the ends of the pole pieces ofthe other yoke half. The facing pole piece ends are spaced apart so asto form magnetic operation gaps. These gaps are aligned along the lengthof the stator.

The armature member or ram is located in the gaps between the statorhalves and is movable relative to the stator in the direction ofalignment of the gaps. The cross section of the ram is substantially thesame as the cross section of the gaps defined by the shapes of the endsof the pole pieces. This cross section can be circular or rectangular.The body of the ram is made from a non-magnetizable material andincludes armature elements of a magnetizable material. The armatureelements extend substantially across the full width of the ram so thattheir cross section is substantially the same as the cross section ofthe ram and of the gaps. When the ram is in its rest position eacharmature element is located adjacent to a respective one of the magneticoperating gaps and the length of each armature element is substantiallyequal to the length of the associated gap. As a result the armatureelements are geometrically shaped so that the volume of each armatureelement is of the order of the volume of the associated gap.

When the ram is in its rest position each armature element is locatedsubstantially outside its associated operating gap. Upon excitation ofthe coil or coils of the stator the resultant magnetic field causes eacharmature element to be pulled into its associated gap and the ram isaccelerated along its length as it is constrained to move in a straightline. A hammer is formed at one end of the ram and this is used toperform a printing operation.

U.S. Pat. No. 4,425,845, describes an arrangement for accommodating aplurality of ram units positioned adjacent to one another into a hammerbank. Each ram unit consists of a flat, narrow frame. A tongue-shapedram, to be driven by an electromagnetic actuator, is slidably receivedin a recess in the frame. For accommodating and guiding the individualprint ram units, the bank is provided with a receiving bar and acomblike holding bar between which the frames of the units are arranged.Extension pieces of the lower elements of the frames are accommodated inslits in the receiving bar. The upper elements of the frames are held inrecesses in the comblike holding bar. Each tongue-shaped ram is guidedlaterally by two electromagnetic actuators which are arranged one oneach side of the frame and are aligned relative to each other.

Such a print hammer bank has a number of disadvantages including that itis expensive to manufacture and its ram units are difficult to exchangeand are susceptible to oscillations.

There is described in IBM Technical Disclosure Bulletin, Volume 25, No11B, April 1983, pages 6284/85 another type of print hammer bank inwhich a plurality of print hammer actuators are positioned adjacent toone another. Each actuator includes a stator having two yoke halves anda movable tongue shaped ram armature member formed at one end with ahammer. The rams are located in a common horizontal plane and for eachram the two stator yoke halves are located on opposite sides of thiscommon plane. The rams extend closely adjacent to one another. Thestator for each ram is wider than the associated ram and thereforeextends beyond the sides of the ram. In order to reduce the overalllength of the hammer bank the stators of adjacent rams are staggered.The stators for one set of rams are positioned towards the hammer endsof the rams and the stators of another set of rams which are interleavedbetween the rams of the first set are positioned towards the other endsof the rams.

The object of the present invention is to provide an improved printhammer bank which is compact and of such a construction that it is easyto replace defective components.

It is another object of the invention to provide a print hammer bankhaving a modular design which tends to eliminate the above mentioneddisadvantages of known types of print hammer bank.

SUMMARY OF THE INVENTION

The invention relates to a print hammer bank made up of modular statorelements. The stator modules are formed in two halves, each halfincluding an electromagnet and a plurality of pole pieces. The statorhalves are interconnected by spaces so that the ends of the pole piecesof the two halves are spaced apart in pairs so as to form a plurality ofaligned operating gaps. A ram including a plurality of armature elementsof magnetizable material is slidably received and guides in tracksformed between the two stator halves in a position so that each of thearmature elements is located adjacent to a respective one of theoperating gaps. The volume of armature elements is sized to be of theorder of the volume of the associated operating gap. When theelectromagnets associated with a particular ram are excited, the ram ismagnetically driven from a rest position in which the armature elementsof the armature member are located outside their respective operatinggaps toward a hammer operating position in which each armature elementis located within its respective operating gap.

The modules are arranged to overlap in a staggered offset fashion thatcontributes to the stiffness of the bank as a whole. This staggeredoverlap is achieved by making the modules of parallelogram or diamondshape so that the parting line between adjacent modules is at asubstantial angle to the direction of ram travel.

Further, the parting line of the upper module halves is not parallel,but transverse to the parting line of the lower module halves.

In addition, the electromagnets associated with the stator halves areconstructed with diamond shaped forms which permit adjacentelectromagnets to be nested compactly together.

The modules are parallelogram or diamond shaped; the gaps betweenadjacent modules in one row coincide with the gaps between adjacentmodules in the other row.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the invention willbe more fully understood by those working in the art by reading andunderstanding the following description of a preferred embodiment of theinvention wherein reference is made to the accompanying drawings, ofwhich:

FIG. 1 is an exploded view of a schematic perspective representation ofthe upper and the lower module rows of a print hammer bank embodying theinvention and having interposed adjacent print hammers,

FIG. 2 is a schematic perspective representation of a module base plate,in which FIG. 2A is a perspective view of the module base plate showingthe side facing the print hammers, and

FIG. 2B is a perspective view of the module base plate of FIG. 2Arotated through 180° about axis 1 showing the side averted from theprint hammers,

FIG. 3 is a plan view of two adjacent print hammer rams in the printhammer bank illustrated in FIG. 1, showing how the actuating armaturebars or elements of the hammers are staggered relative to each other,

FIG. 4 is an exploded view of a schematic perspective representation ofthe electromagnet assembly used in the print hammer bank illustrated inFIG. 1 and consisting of two U-shaped yokes which are positionedadjacent to each other with their adjacent legs encompassed by a coil,

FIG. 5 is a perspective view of two adjacent module base plates of theupper module row of the print hammer bank illustrated in FIG. 1 showingthe side of each module base plate facing the print hammers,

FIG. 6 is a perspective view of two adjacent module base plates of thelower module row of the print hammer bank illustrated in FIG. 1 showingthe side of each module base plate facing the print hammers, and

FIG. 7 is a schematic perspective representation of a print hammerpositioned between the upper and the lower module rows of the printhammer bank illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an exploded view of a schematic perspective representation ofthe lower and the upper module rows of a print hammer bank embodying theinvention and having interposed adjacent print hammers.

The print hammer bank is made up of identically shaped modules 7, 8, 9,10. Each module in plan view is shaped like a parallelogram or diamond.Each module consists of a module base plate (e.g. 11 in the case ofmodule 7) and a stator member 12 connected thereto. Electromagnetassemblies 30 (FIG. 4) are located in and molded to the stator member12. Adjacent modules 9 and 10 form an upper row 3 and adjacent modules 7and 8 form a lower row or portion 4. The upper module row or portion 3and the lower module row 4 are spaced from each other as shown ingreater detail with respect to FIG. 7.

Two print hammers, 5 and 6, are shown in FIG. 1. The print hammers aresupported adjacent to each other between the upper module row and thelower module row for movement in the direction of arrow D. On the sidefacing the print hammers, each module 7, 8, 9, 10 has a plurality ofpole faces PF of the electromagnet yokes. The pole faces of the uppermodule row are aligned with those of the lower module row in pairs. Thespaced pairs of pole faces of the upper and the lower module rows definea plurality of magnetic operating gaps. These operating gaps areactivated by electromagnetic coil excitation.

The pole faces PF are arranged in tracks or columns (C) associated withindividual print hammers. In FIG. 1, each column of a module has fourpole faces. Each print hammer (illustrated in FIG. 3) has as many softiron bars (armature bars or elements) as there are operating gapsdefined by the pole faces in its associated columns. In the print hammerdescribed, the number of soft iron bars is four. The spacing of thesoft-iron bars in each print hammer corresponds to the spacing of theoperating gaps in the associated columns of the print hammer bank sothat each soft iron bar is associated with a respective operating gap.The soft iron bars are designed so that the volume of each soft iron baris of the order of the volume of its associated operating gap.

When each print hammer is in its rest position, each soft-iron bar inthe hammer is positioned outside its associated operating gap. When themagnetic operating gaps for each print hammer are activated byenergising the associated electromagnetic coil, the armature bars of theprint hammer are pulled into the operating gaps. The print hammer isaccelerated in this process in the direction of print illustrated by thearrows D.

The modules of each module row are positively connected to each other.For forming the operating gaps, the modules of the upper module row 3and the modules of the lower module row 4 are spaced from each other byspacer elements (see FIG. 7). The modules of the upper row 3 and thelower row 4 are held in place by screws or rivets or similar joiningdevices. Such joining devices may extend, for example, through thearrow-marked through holes P1/P2, P3/P4, P5/P6, P7/P8. On the side ofeach module averted from the print hammers, a plurality of connectorpins 46 are provided for connection to the electromagnet assemblies. Theelectromagnet assemblies, the spacer elements for the module rows, thepositive connection of the modules within a row and the layout andstructure of the modules will be described in greater detail below.

The lines 84 defining the boundaries between adjacent columns or tracksC will be described in detail below with reference to FIG. 7.

The shapes of the modules in plan view are identical and are based on amodified parallelogram. This design provides a high packing density ofthe print hammers. The pole faces of the electromagnet assemblies inadjacent columns are staggered relative to each other and the armaturebars or elements of adjacent print hammers are also staggered relativeto each other to cooperate with the staggered pole faces. If the shapesof the modules in the print hammer bank are identical in both the upperand the lower module rows, the number of print hammers for each moduleis invariably even.

FIG. 4 is an exploded view of a schematic perspective representation ofone of the electromagnet assemblies used in the print hammer bank. Theelectromagnet assembly consists of two adjacent U-shaped yokes 31 and32, whose adjacent legs are encompassed by a common coil 45 illustratedon a coil carrier. The coil carrier consists of a cuboid or diamondshaped base plate 50 and a similarly shaped upper cover plate 49. Theseplates are linked to each other by two spacer elements 48 and acentrally positioned hollow body 81. Below the base plate, the spacerelements 48 are connected to connector pins 46 forming electricalconnections to the coil 45. The base plate 50 has openings 74 and 75through which the outer yoke legs of the yoke pair 31, 32 are inserted,and an opening in the region of the hollow body 81 for accommodating theadjacent inner yoke legs of the yoke pair 31, 32. The cover plate 49 hasfour openings 41, 42, 43, 44 for accommodating the pole faces 31-1,31-2, 32-1, 32-2 of the yokes 31 and 32. After the yokes have beeninserted into the coil body and fixed in position, for instance byplastic molding, the ends of the yoke legs project slightly above theupper cover plate 49. If the plastic used for molding is a material witha good thermal conductivity the heat dissipation within the print hammerwill be good. How the electromagnet assemblies and the module baseplates are connected to each other is described below.

FIGS. 2A and 2B are schematic perspective representations of one modulebase plate, FIG. 2A showing the side facing the print hammers and FIG.2B the side averted from the print hammers. FIG. 2B shows the modulebase plate of FIG. 2A rotated through 180° about the axis 1. While FIG.2A is a perspective plan view of the module base plate, viewed in thedirection U, FIG. 2B is a plan view of its lower side, viewed in thedirection B. Each electromagnet assembly is assembled onto its top coverplate 49 on the rear side of the associated module base plate bymovement in the direction B. The yoke leg ends project slightly throughthe openings 41, 42, 43 and 44 beyond the cover plate 49 of theelectromagnet assembly and fit into the corresponding openings of acolumn in the module base plate. The pole faces of yoke pair 31, 32 inthe openings of the first and the second columns in FIG. 2A aredesignated as (32-1), (32-2), (31-1) and (31-2) consistent with FIG. 4.The yoke leg ends are introduced into these openings until the coverplate 49 fits flush with the plane of the rear face of the module baseplate 11.

The electromagnet assemblies for adjacent module columns are staggeredfore and aft relative to each other to ensure a high packing density.Therefore, the pole faces of adjacent module columns are also staggeredrelative to each other. Two electromagnet assemblies staggered relativeto each other are shown in FIG. 2B by the broken line diamond shapedcontours of their cover plates. It will be noted that the width of eachelectromagnet assembly is greater than the width of the correspondingcolumn and armature member but that the diamond shapes of theelectromagnet assemblies and their staggered relative positioning allowsthe electromagnet assemblies to be located partially overlapping so asto account for their greater width.

FIG. 5 is a perspective representation of two adjacent module baseplates of the upper module row, looking at the sides of the base platesfacing the print hammers. The left base plate 9 has extensions 93 and 94on its left side and recesses 91 and 92 on its right side. For the rightbase plate 10 the extensions are designated as 103, 104 and the recessesas 101 and 102. The extensions and recesses are shaped so that theypositively fit each other.

FIG. 6 is a perspective view of two adjacent module base plates 7 and 8of the lower module row, looking at the sides of the base plates facingthe print hammers. It will be appreciated that these lower base platesare substantially identical to the upper base plates illustrated in FIG.5 and will not be described in further detail.

In the assembled print hammer bank, the upper module base plates 9 and10 of FIG. 5 will be rotated through 180° about the assumed axis 2 sothat a space accommodating the print hammers is formed between thesemodule base plates in the rotated state and the lower module base plates7, 8 of FIG. 6. Since the individual modules are all identical andparallelogram shaped in plan view, the upper modules will form atransverse angle with the lower modules and the joints between adjacentmodules in the upper row of modules will only coincide with the jointsbetween adjacent modules in the lower module row over short distances.As a result the structure of the print hammer bank will be stiff. If adefect occurs in any actuator, the module in which the defectiveactuator is located can be removed and the actuator and/or the modulerepaired or exchanged for a new one without affecting the rest of theprint hammer bank.

FIG. 7 is a schematic perspective view of a print hammer positionedbetween the upper and the lower module rows. The portion of the modulebase plate of the upper row illustrated is designated as 80 and that ofthe lower module row as 70. The upper and the lower module rows arespaced from each other by spacers 83 positioned in grooves 82 formed inthe upper and lower module base plates. The positions of these groovesand spacers correspond to the column boundaries marked by parallel lines84 in FIG. 1 and physically form the tracks or spaces in which thehammers, such as hammer 5, are movably positioned. The operatingdirection of movement of the print hammer is marked by arrow D.

Details of two adjacent print hammers are shown in FIG. 3. This is aplan view of two print hammers arranged adjacent to each other in theprint hammer bank and shows that the armature bars or elements used fortheir actuation are staggered relative to each other. The armature barsof the print hammer 5 are designated as 51, 52, 53 and 54. They areassociated with the operating gaps which are defined, for instance, bythe pole faces 32-1, 32-2, 31-1 and 31-2 (FIG. 2A) of the left handcolumn of the base plate 9 of the upper module row and the cooperatingpole faces of the base plate 7 of the lower module row which are alignedwith the upper pole faces (FIGS. 1 and 2). This applies also to theprint hammer 6 which is illustrated as having armature bars 61, 62, 63,64. These armature bars are associated with the pole faces 32-1, 32-2,31-1, 31-2 of the second column (FIGS. 1 and 2). The print hammers 5 and6 have recesses 55, 56, 66 and 65 to reduce their weight. Theiroperating ends are provided with print hammer heads 57 and 67respectively.

The print hammers are restored to their rest positions after actuationin a conventional manner, for example, by a leaf spring engaging in asuitable one of the recess 55, 56 or 66, 65. These recesses or the endsof the print hammers facing the print hammer heads 57, 67 may also beprovided with dampers or detents for defining the starting or restposition of each print hammer.

What we claim is:
 1. A modular print hammer bank comprising a pluralityof stator modules assembled into a lower stator portion and a furtherplurality of stator modules assembled into an upper stator portion,meansinterconnecting said upper and lower stator portions to form a series ofrectilinearly extending track spaces therebetween, the modules of eachportion having mutually adjacent side edges that extend at an anglesubstantially greater than zero degrees with respect to said rectilineartrack spaces, the side edges of the modules of the upper portionextending at an angle substantially greater than zero degrees withrespect to the adjacent side edges of modules of the lower portion andwherein each module of said upper portion overlies and is connected toat least two modules of the lower portion, a plurality of rams movablypositioned individually in different ones of said track spaces, each ofsaid rams comprising a non-magnetic body and at least a pair ofmagnetizable armature pieces carried by said body, and said modulesfurther comprising a plurality of electromagnets carried by said statorportions in opposed pairs adjacent individual track spaces, each of saidelectromagnets providing at least a pair of pole faces positionedadjacent individual armatures pieces of associated rams.
 2. A modularprint hammer bank as defined in claim 1 wherein said modules aresubstantially identical and are formed in the shape of parallelogramswith one pair of included angles being substantially greater than aright angle and the other pair of included angles being substantiallyless than a right angle.
 3. A modular print hammer bank as defined inclaim 2 wherein at least some of said track spaces overlie said angledside edges, at least four electromagnets being associated with each ofsaid track spaces, two of said electromagnets being carried by modulesof said upper stator portion and two of said electromagnets beingcarried by modules of said lower stator portion, andwherein the twoupper stator portion electromagnets and the two lower stator portionelectromagnets associated with a track space that overlies an angledside edge are each separately carried by adjacent ones of said modules.